Protein solubility is increased by antioxidant addition during protein extraction from the green macroalga, Ulva sp.

Abstract

Ulva sp. is a cosmopolitan green macroalga with fast growth and a well-balanced amino acid composition, making it an interesting potential protein resource. Generally, the protein digestibility in unprocessed raw seaweed is low, which is why extraction and concentration of the protein is needed. During protein extraction from fresh Ulva sp. using double screw pressing, sulfite was added as antioxidant in order to increase protein quality by inhibiting oxidative reactions. By pressing, 13–14% of the total biomass protein was extracted. Isoelectric precipitation at pH 2 resulted in a yield of 36% of the extracted protein corresponding to 5% of the total protein, independent on sulfite treatment. However, size exclusion chromatography showed that sulfite addition resulted in a higher amount of native state Rubisco protein. This was explained by inhibited redox enzyme activity and improved polyphenol levels, suggesting prevention of polyphenol-protein crosslinking, resulting in higher amount of soluble protein and improved protein quality.